No probs - I'm grateful for your time.  And it works now, that's the great thing.

Thanks, Cavalcader, but I think you might have been in a hurry, and didn't read my full post.  I wrote:

'So I clicked on "Launch application", and - nothing happened.  For 10 minutes, until I gave up waiting.  then I went to the folder where I had saved it and tried opening it from there.  And got the same error message I originally started with - "file is not a valid Win32 application".'

So I have tried both of your suggestions, with no luck.  That's why I'm giving up and am now looking for a program that will actually install on my computer.

BTW, in my experience Firefox does not always give a warning like this, which refers to an external app being launched - it usually just warns that the file is executable.

Thanks for the tip about the IE cache - I have done that.  I also downloaded the file via Firefox - and it was 8.1MB.  But now another problem, I'm afraid - I tried opening it from the Firefox download manager, and got the message attached.  So I clicked on "Launch application", and - nothing happened.  For 10 minutes, until I gave up waiting.  then I went to the folder where I had saved it and tried opening it from there.  And got the same error message I originally started with - "file is not a valid Win32 application".

I'm sinerely grateful for all your help, but I'm now giving up.  When a program is this difficult to get started - even with all the valuable help on this site - I lose interest.  I'm not so desperate for it that I want to devote hours or days of my life to getting it to even install.

But thanks, guys, for all your suggestions.  At least I've learned to empty the IE cache!

Now I'm going to google for a screen capture program I can use.

All the best